Determination of the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to a standardised noxious stimulus in goats

Abstract

OBJECTIVE : To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to noxious stimulation. STUDY DESIGN : Prospective, experimental.Animals Eight healthy goats; four does and four wethers. METHODS : Anaesthesia was induced with alfaxalone 3 mg kg 1 intravenously (IV). A continuous IV infusion of alfaxalone, initially at 0.2 mg kg 1 minute 1, was initiated. Following endotracheal intubation the goats breathed spontaneously via a circle breathing circuit delivering supplementary oxygen.The initial infusion rate was maintained for 30 minutes before testing for responses. The stimulus was clamping on the proximal (soft) part of one digit of the hoof with Vulsellum forceps for 60 seconds. In the absence or presence of purposeful movement of the extremities, the infusion ratewasreduced or increased by 0.02 mg kg 1 minute 1 and held constant for 30 minutes before claw-clamping again. Alfaxalone MIR was calculated as the mean of the infusion rates that allowed and abolished movement. Cardiorespiratory parameters were measured. Recovery from general anaesthesia was timed and quality scored. Results are presented as median (range). RESULTS : The MIR of alfaxalone was 0.16 (0.14– 0.18) mg kg 1 minute 1 or 9.6 (8.4–10.8) mg kg 1 hour 1. Induction of and recovery from anaesthesia were excitement-free. Cardio-respiratory changes were minimal, although compared to baseline HR increased, and at 2 minutes postinduction,(prior to oxygen supplementation), PaO2 decreased significantly from 84 (80–88) to 70 (51– 72) mmHg [11.2 (10.7–11.7) to 9.3 (6.8–9.6) kPa]. Sporadic muscle twitches, unrelated to depth of anaesthesia, were observed during the period of general anaesthesia. Time (minutes) to sternal recumbency and standing were 4.0 (3.0–10.0) and 41.5 (25.0–57.0) respectively. CONCLUSIONS AND CLINICAL RELEVANCE : Alfaxalone can be used for total intravenous anaesthesia (TIVA) in goats and is associated with minimal adverse effects. Oxygen supplementation is advised, especially when working at higher altitudes.